1. Field of the Invention
The present invention relates to a regulated amount measuring apparatus for indicating a difference between two colors, for example, a discrepancy between a color of a printed matter in proof and a target color, to provide an index for a color regulation, and a regulated amount measuring program storage medium storing a regulated amount measuring program, which causes an arithmetic processing apparatus such as a computer to operate as the regulated amount measuring apparatus.
2. Description of the Related Art
Hitherto, as an ink control process of a multi color offset press, it is generally performed that the substantially four steps of regulation, as set fourth below, are carried out to meet the target color of a proof sheet.
(1) Perform a mechanical regulation for a printing machine such as printing pressure.
(2) Contribute to optimization of a supply of moistening water in the actual printing.
(3) Monochromatic solid or monochromatic halftone of image is provided on a portion out of a printed image on a sheet, for example, a blank, and the optical density of this portion is measured so that an ink supply is controlled to meet the density control value obtained through experience.
(4) An operator of the printing machine performs on a visual basis an ink supply control to finally meet the proof image.
To perform the ink supply control in the item (4), there is a need for the operator to meet the proof image on a visual basis. Thus, there is a need to control ink supply for plates of cyan (C), magenta (M) and yellow (Y). At that time, for example, when a printed matter, which takes on a Y-tinge more than the proof image, is regulated, a decision as to whether a supply of Y-ink is to be suppressed, whether amounts of M-ink and C-ink are to be increased, or alternatively whether a supply of Y-ink is to be suppressed and in addition amounts of M-ink and C-ink are to be increased, is a difficult judgement in such an extent that only the skilled operator can do it.
As a device for measuring colors, there is known a calorimeter. The use of the calorimeter makes it possible to measure colors so as to obtain calorimetric values of CIEXYZ and L*a*b*, and catch a direction of discrepancy of a color. However, there is a rare operator who can read regulating amounts for ink of C, M and Y from the calorimetric values of CIEXYZ and L*a*b*.
As technique of automatically computing regulating amount of ink, Japanese Patent No. 2505434 discloses a method in which a relation of a partial differential between a color difference and a density difference of each of inks for C, M and Y in a target color gamut is measured beforehand, and instead of the measurement of ink density of the above-mentioned item (3), a chromaticity measurement of three color gray patch is carried out to compute a difference from chromaticity of proof, and the ink regulating amount is computed so that the computed difference from chromaticity of proof is minimum. According to the method disclosed in Japanese Patent No. 2505434, however, it is obliged to obtain data for the ink-regulating amount after the target color gamut is determined beforehand, and it is difficult in regulation of an arbitrary color. Thus, actually, in putting into practice, there is a need to determine control colors, such as multiplying halftone of 60% for instance, for C, M and. Y, respectively. To the contrary, in case of the actual printed matter, it is often happened that the important color is varied in accordance with the printed matter. And thus, according to the method disclosed in Japanese Patent No. 2505434, it is difficult to adequately cope with the printed matter.
Further, the method disclosed in Japanese Patent No. 2505434 is involved in putting into practice at the stage of a rough regulation of the ink supply. And thus to perform a fine regulation of colors, it is obliged to trust a skilled operator's experience and intuition.